polymer with water as the base and sand or another suitable proppant. Further
fracturing boreholes are gradually added to the site, till the target region is fully
fractured. Theoretically, hydraulic fracturing may be carried out in boreholes without casing, using a system of packers. In this way, even several fractured areas
located one above the other may be formed, wherein the required vertical interval
between the individual areas is usually in the range from 1.0 to 2.0 m. The expected
speed of crack formation is usually at the level of ca 0.1 m/s. The necessary
technological equipment is commonly available in oil drilling and mining companies. However, the equipment is usually intended for much higher requested outputs
than the ones necessary in the remediation practice. Thus, a smaller and simpler
equipment has been developed for remediation purposes.
Depending on the application depth, either a vertically or horizontally oriented
crack is formed. At a depth up to 30 m, which is common for remediation practice,
formation of a vertically oriented crack is practically excluded. The formed crack
may be oriented in a different than horizontal way only if the natural geological
environment layers are thus oriented.
In the case of unconsolidated geological materials, a proppant is always added
into the fracturing mixture. For a pressure injection, the proppant must be always
kept in a suspension. This is achieved either through intensive mixing or through
addition of other additives and the fracturing liquid (Zeidler and Pašiak 1986). In this
way, a cross-linked polymer (gel) is formed, which is able to maintain its structure
for the necessary time period (ca 12–24 hours). After this time period, it disintegrates
to a liquid showing viscosity similar to water, which enables its subsequent washing
out of the geological environment. A various spectrum of liquid as well as solid
materials may be used for hydraulic fracturing thanks to which a very quick single
injection of suitable auxiliary substances for implementation of in situ remediation
methods may be achieved (Siegrist et al. 2001).
32.4 Feasibility Limits of Fracturing Methods
Suitability of utilization of the fracturing for supporting remediation measures is
influenced, in particular, by the following geotechnical conditions of the geological
environment:
• Kind of the environment: The final effect of the fracturing may be estimated in
advance. The highest efficiencies are achieved in a compact environment showing low permeability, such as fine-grained sedimentation materials.
• Permeability of the environment: The most frequent application of fracturing is a
targeted increase in aquifer permeability, and thus the impact of remediation.
The general rule is that the smaller the permeability, the higher efficiency of
procedures for fracturing is achieved, and vice versa.
• Depth of the area of interest: Theoretically, there is no depth limit for creating
new fractures in the geological environment that would ensure sufficient flow and
pressure applied to the area of interest. In the remediation practice, the depth can
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J. Kukačka and P. Kvapil
fracturing boreholes are gradually added to the site, till the target region is fully
fractured. Theoretically, hydraulic fracturing may be carried out in boreholes without casing, using a system of packers. In this way, even several fractured areas
located one above the other may be formed, wherein the required vertical interval
between the individual areas is usually in the range from 1.0 to 2.0 m. The expected
speed of crack formation is usually at the level of ca 0.1 m/s. The necessary
technological equipment is commonly available in oil drilling and mining companies. However, the equipment is usually intended for much higher requested outputs
than the ones necessary in the remediation practice. Thus, a smaller and simpler
equipment has been developed for remediation purposes.
Depending on the application depth, either a vertically or horizontally oriented
crack is formed. At a depth up to 30 m, which is common for remediation practice,
formation of a vertically oriented crack is practically excluded. The formed crack
may be oriented in a different than horizontal way only if the natural geological
environment layers are thus oriented.
In the case of unconsolidated geological materials, a proppant is always added
into the fracturing mixture. For a pressure injection, the proppant must be always
kept in a suspension. This is achieved either through intensive mixing or through
addition of other additives and the fracturing liquid (Zeidler and Pašiak 1986). In this
way, a cross-linked polymer (gel) is formed, which is able to maintain its structure
for the necessary time period (ca 12–24 hours). After this time period, it disintegrates
to a liquid showing viscosity similar to water, which enables its subsequent washing
out of the geological environment. A various spectrum of liquid as well as solid
materials may be used for hydraulic fracturing thanks to which a very quick single
injection of suitable auxiliary substances for implementation of in situ remediation
methods may be achieved (Siegrist et al. 2001).
32.4 Feasibility Limits of Fracturing Methods
Suitability of utilization of the fracturing for supporting remediation measures is
influenced, in particular, by the following geotechnical conditions of the geological
environment:
• Kind of the environment: The final effect of the fracturing may be estimated in
advance. The highest efficiencies are achieved in a compact environment showing low permeability, such as fine-grained sedimentation materials.
• Permeability of the environment: The most frequent application of fracturing is a
targeted increase in aquifer permeability, and thus the impact of remediation.
The general rule is that the smaller the permeability, the higher efficiency of
procedures for fracturing is achieved, and vice versa.
• Depth of the area of interest: Theoretically, there is no depth limit for creating
new fractures in the geological environment that would ensure sufficient flow and
pressure applied to the area of interest. In the remediation practice, the depth can
628
J. Kukačka and P. Kvapil